1. Field of the Invention
The invention relates to a light source. More particularly, the invention relates to a light emitting diode (LED) bulb having uniform brightness.
2. Description of Related Art
The light emitting diode (LED) is extensively used in light bulbs, and such development matches the trend for low power consumption and environmental protection. However, since the LED has the light source output characteristics such as spot light source, high brightness, and narrow light beams, and considerations such as mechanical properties and product reliability for LED differ from traditional lamp products, countries all over the world are developing testing standards for fixture lighting including street lamps, outdoor illumination, interior lighting, etc.
There are few light emitting diode bulbs currently on the market that meet the standard for Energy Star. The main reason lies in that the LED itself provides light having strong directional property. That is, light from the LED is emitted in a certain direction. Furthermore, the position of the LED in the light bulb is affected and limited by the internal driving circuit and heat sink. In general, the light emitting angle of a high power LED for illumination is mostly 120 degrees. How to design an LED light bulb having a wide light emitting angle in terms of the structure and the optical design while still having a uniform and sufficient brightness is indeed a goal most manufacturers strive for.
FIG. 1A is a schematic view of a conventional LED bulb, and FIG. 1B is a schematic view of a light field distribution of the LED bulb shown in FIG. 1A. Referring to FIG. 1A and FIG. 1B, a lamp cover 110 of a conventional LED bulb 100 is usually semispherical. As such, when light provided by LEDs (not shown) in the bulb 100 passes through the lamp cover and is emitted from the bulb 100, the distribution of the light field is overly concentrated in the center such that the uniformity and the light emitting angle is not ideal.